1. Field of the Invention
The present invention relates to a color image forming apparatus and a method of controlling the same that carry out a developing process by moving a developing unit in which developing devices corresponding to a plurality of image formation colors are incorporated, as well as a control program for implementing the method.
2. Description of the Related Art
Conventionally, there has been known a rotary developing type full-color image forming apparatus that carries out a developing process by rotating a developing rotary unit in which a plurality of developing units corresponding to respective image formation colors are incorporated.
FIG. 9 is a diagram schematically showing the construction of a conventional rotary developing type full-color image forming apparatus of this type.
The full-color image forming apparatus in FIG. 9 is comprised of a color reader section 400 that scans the entire surface of an original to read an image thereon in full color, and a color printer section 500 that prints out color image data read by the color reader section 400.
The color printer section 500 is comprised of a developing rotary 503 in which developing devices 503Y, 503M, 503C, and 503K corresponding to respective four colors (yellow, magenta, cyan, and black) are incorporated. A laser scanner 501, which is installed in the color printer section 500, scans a laser beam corresponding to image data generated by the color reader section 400 and irradiates the laser beam onto a photosensitive drum 502. As a result, an electrostatic latent image is formed on the photosensitive drum 502.
When the electrostatic latent image on the photosensitive drum 502 reaches the position of a sleeve of a predetermined color among sleeves 53Y, 53M, 53C, and 53K corresponding to the respective image formation colors in the developing rotary unit 503, a toner of the predetermined color is jetted from the concerned developing device to the surface of the photosensitive drum 502, so that the electrostatic latent image on the surface of the photosensitive drum 502 is developed. Then, the toner image formed on the photosensitive drum 502 is transferred onto an intermediate transfer member 505. In the case where the read image is a full color image, the sleeves of the respective colors are sequentially positioned at a predetermined location that is to face the electrostatic latent image on the photosensitive drum 502 by rotating the developing rotary unit 503, to develop/transfer electrostatic latent images corresponding to the respective colors on the photosensitive drum 502.
On the other hand, a recording sheet picked up from a cassette 508 is conveyed to a nip between the intermediate transfer member 505 and a transfer roller 506 in timing with the completion of the transfer to the intermediate transfer member 505. Then, the recording sheet is conveyed toward a fixing device 510 and attached under pressure to the intermediate transfer member 505 at the same time, and as a result, the toner image on the intermediate transfer member 505 is transferred onto the recording sheet. The toner image transferred onto the recording sheet is fixed onto the recording sheet by heating and pressurizing by fixing rollers of the fixing device 510 and pressurizing rollers 507.
As stated above, in the rotary developing system of the conventional full-color image forming apparatus, the sleeves of the respective colors are sequentially positioned at the predetermined location by rotating the developing rotary unit 503 such that the respective sleeves sequentially face the electrostatic latent image on the photosensitive drum 502, and then the developing process is carried out. In forming an image, the developing rotary unit 503 is rotated using a stepping motor so as to change image formation colors (yellow, magenta, cyan, and black).
However, there occur variations in the amounts of color toners consumed depending on secular changes of the image forming apparatus and distribution of colors in images formed, and this leads to increased vibrations created by the developing rotary unit 503 when it starts or stops rotating. As a result, the vibrations created by the developing rotary unit 503 are transmitted to the laser scanner 501, the photosensitive drum 502, the intermediate transfer member 505, and so forth to shift the laser irradiation position and cause splash of toners. This adversely affects the quality of images formed.
To cope with deterioration in image quality caused by such vibrations during image formation, there have been proposed a method in which an image forming operation is inhibited or temporarily halted depending on the level of vibrations during image formation (see Japanese Laid-Open Patent Publication (Kokai) Nos. H05-019558 and H08-146843), and a method in which vibrations that have occurred are canceled out by creating vibrations in opposite phase to the vibrations that have occurred (see Japanese Laid-Open Patent Publication (Kokai) No. H11-194608 and U.S. Pat. No. 6,060,813).
However, where the full-color image forming apparatus is connected to a network and remotely used as a printer, it is desirable to reduce the frequency with which the image forming apparatus is stopped to the minimum possible level while it is in use. In this example, adopting the above method in which an image forming operation is inhibited or temporarily halted so as to cope with deterioration in image quality caused by vibrations created during image formation interferes with smooth usage of the image forming apparatus.
Also, in the above method in which vibrations in opposite phase to vibrations that have occurred are created, a sensor with high responsiveness and accuracy and a device for creating vibrations are required, and hence the image forming apparatus is complicated in construction and expensive, and in addition, excess electric power is needed to create vibrations.
In view of the foregoing, a full-color image forming apparatus that is capable of continuing to carry out an image forming operation even when vibrations occur, and is inexpensive and simple in construction is desired.